Factorial Calculator

Few functions grow like the factorial. 10! is 3.6 million; 20! is 2.4 quintillion; 100! has 158 digits; 100000! has over four hundred and fifty thousand. The factorial quietly powers the mathematics of counting - permutations, combinations, probability, series - while its own value outgrows every ordinary calculator by the time n reaches 70, where floating point simply gives up.

Factorial Calculator never gives up. It computes n! exactly with BigInt arithmetic up to 100000!, reporting the digit count, the first and last digits, the number of trailing zeros - computed instantly by counting factors of 5 - and the full value on demand for manageable results. Growth, counting and probability share one exact engine.

• Exact to 100000!: BigInt arithmetic, never approximate.
• Digit count: The growth rate made visible.
• Trailing zeros: Instant via factors of 5, explained.
• First and last digits: The extremes of a huge number at a glance.
• Full value on demand: For results up to a few thousand digits.
• Instant results: Live as you type.
• Copy or download: The value travels with you.
• Free and private: Everything runs in your browser; nothing is uploaded.

1. Enter n - from 0 to 100000.
2. Read the headline - n! with its digit count.
3. Check the trailing zeros and the first and last digits.
4. Toggle the full value if you need every digit.
5. Copy or download what you need.

Example 1 - The basics. Enter 5: 5! = 120, one trailing zero, three digits.

Example 2 - The classroom favorite. Enter 10: 10! = 3,628,800, with the first and last digits shown.

Example 3 - Where calculators fail. Enter 70. Floating-point calculators lose exactness here; the tool returns 70! with all 101 digits exact.

Example 4 - The trailing-zero puzzle. Enter 100: 100! has 24 trailing zeros - the count of factors of 5 in 1 to 100, shown instantly.

Example 5 - The monster. Enter 100000: 456,574 digits, and the first digits 28242294079... - a number no ordinary calculator can even hold.

• Exact always: BigInt arithmetic to 100000!.
• Instant insights: Digits, zeros, extremes in one view.
• Growth made visible: The digit count tells the story.
• Full value when needed: No arbitrary precision limits.
• Instant and live: No button presses, no waiting.
• Free and private: Runs entirely in the browser with nothing uploaded.